The Natural Organic Colouring Matters
By
Arthur George Perkin, F.R.S., F.R.S.E., F.I.C., professor of colour chemistry and dyeing in the University of Leeds
and
Arthur Ernest Everest, D.Sc., Ph.D., F.I.C., of the Wilton Research Laboratories; Late head of the Department of Coal-tar Colour Chemistry; Technical College, Huddersfield
Longmans, Green and Co.
39 Paternoster Row, London
Fourth Avenue & 30th Street, New York
Bombay, Calcutta, and Madras
1918
Kaikki kuvat (kemialliset kaavat) puuttuvat // None of the illustrations (of chemical formulas) included.
This important yellow dyestuff, the latest addition to the somewhat meagre list of commercial natural colouring matters, was discovered and introduced by Bancroft in 1775. In his "Philosophy of Permanent Colours" he states (ii., 113): "Quercitron bark is one of the objects of a discovery of which the use and application for dyeing are exclusively vested in me, for a term of years by an Act of Parliament in the twenty-fifth year of his present Majesty's reign".
Quercitron bark is the inner bark of a species of oak known as Quercus discolor; Ait (Q. tinctoria), which is a native of the Middle and Southern States of America. The tree in the south is described as being from 60 to 80 feet high, with a trunk from 6 to 10 feet in diameter; but in the north it does not attain to this size. In order to obtain the dyestuff the epidermis or exterior blackish coat of bark is usually removed by shaving and the inner portion then detached and ground. The product may be separated into stringy fibres and a light fine powder, the latter of which contains the principal portion of the colouring matter.
Quercitron bark and its preparations are still used to a considerable extent, although not so much as was formerly the case. This is not only due to the introduction of the artificial colouring matters, but because it has been supplanted for many purposes by the less costly old fustic.
Quercetin, C15H10O7;, the colouring matter of quercitron bark, has been the subject of numerous researches, and many of these unfortunately resulted in the publication of complicated and unsatisfactory formulæ. At an early stage it was ascertained that quercetin does not exist in the plant, at least to any extent in the free condition, but in the form of its glucoside quercitrin.
To prepare quercetin the following method devised by the late Sir W. H. Perkin, and employed by him for several years on the manufacturing scale, gives good resets. Quercitron bark dust is macerated with moderately strong salt solution to remove gummy substances, filtered, and then extracted with dilute ammonia. The cold ammoniacal liquid is treated with a slight excess of hydrochloric acid, causing the separation of certain impurities in the form of a brown flocculent precipitate. This is removed, and the pale yellow acid solution of the glucoside is boiled for about thirty minutes. The glucoside is thus hydrolysed and almost chemically pure quercetin separates in the form of pale yellow needles, which are collected while the mixture is still warm and washed with water. It is readily soluble in alcohol, and dissolves in alkaline solutions with a yellow colour. With aqueous lead acetate it gives a bright orange- red precipitate, and with alcoholic ferric chloride a dark green colour.
The most important of the early investigations of quercetin was carried out by Liebermann and Hamburger (Ber., 12, 1178), who assigned to it the formula C24H16O11 and to quercitrin the formula C26H38O20 Herzig (Monatsh., 5, 72; 6, 863; 9, 537; 12, 172; 14, 53; 15, 697), who made an elaborate series of researches on this subject, at first adopted this formula. Subsequently it was ascertained that quercetin was in reality C15H10O7, and this receivedsupport by the examination of its compounds with mineral acids (Perkin and Pate, Chem. Soc. Trans., 1895, 67, 647).
When quercetin is fused with alkali, it gives protocatechuic add and phloroglucinol, and if its alkaline solution is oxidised with air, the same products are obtained. By the more gentle action of the alkali, Hlasiwetz and Pfaundler (Jahres., 1864, 561) obtained certain intermediate products of the hydrolysis, paradiscetin, C15H10O6, yellow needles, quercetic acid, C15H10O7, colourless needles, and quercimeric acid, C8H6O5, H2O, colourless crystals. Herzig and others who have reinvestigated this decomposition have been unable to obtain the substances of Hlasiwetz and Pfaundler, and if these compounds are in reality chemical individuals, it seems likely that their formation was due to the action of some special impurity contained in the alkali employed by these chemists.
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Quercetin is a strong dyestuff, and gives with mordanted wool the following shades, which are almost identical with those produced by fisetin:
Chromium. Red-brown.
Aluminium. Brown-orange.
Tin. Bright orange.
Iron. Olive-black.
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Quercitrin, the glucoside of quercetin, was first isolated from quercitron bark by Chevreul, and has been examined by numerous chemists. The method usually employed for the preparation of this substance is that devised by Zwenger and Dronke (Annalen, Suppl., 1, 267), and this was subsequently utilised by Liebermann and Hamburger (Ber., 12, 1179).
Quercitron bark is extracted with 5-6 times its weight of boiling 50 per cent, alcohol, the extract evaporated to one-half, and treated with a little acetic acid, followed by lead acetate solution. The precipitate is removed, sulphuretted hydrogen is passed through the filtrate, and after removal of lead sulphide the clear liquid is evaporated to dryness. The residue is dissolved in a little hot alcohol, the solution treated with water and the crude quercitrin which separates on cooling is purified by repeated crystallisation from water.
A very convenient source of quercitrin is yellow flavine (Perkin, private communication), which consists almost entirely of this substance, and is usually free from quercetin. A hot aqueous extract of this material gives, on cooling, a crystalline precipitate of the glucoside, and this by recrystallisation from water with the aid of animal charcoal is readily obtained pure.
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It was formerly considered that the glucosides (colouring principles) were hydrolysed during the dyeing operation, and that the shades thus obtained were due not to the glucosides, but to the free colouring matters. This in certain cases is correct, especially when the plant contains an enzyme capable of effecting the hydrolysis; but on the other hand, in many cases the glucoside is itself the colouring matter and directly responsible for the dyeing effect. Quercitrin is an instance in point (Perkin, Chem. Soc. Trans., 1902, 81, 479), and gives upon mordanted fabrics shades which are distinct from those of quercetin itself.
Quercitrin.
Chromium - Full brown-yellow.
Aluminium - Full golden-yellow.
Tin - Lemon-yellow.
Iron - Deep olive.
Quercetin.
Chromium - Red-brown.
Aluminium - Brown-orange.
Tin - Bright orange..
Iron - Olive black.
Kaempferol.
Chromium - Brown-yellow.
Aluminium - Yellow.
Tin - Lemon-yellow..
Iron - Deep olive-brown.
In dyeing property quercitrin very closely resembles kaempferol, and, indeed, differs but little from morin (old fustic) and luteolin (weld) in this respect. It was thus probable, according to Perkin (loc. cit.), that the constitution of the glucoside is to be represented by one of the two following formulæ: [KUVA PUTTUU]
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The colours given by quercitrin are somewhat faster than those derived from quercetin.
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